Carbon-fiber-reinforced plastics (CFRPs), which contains carbon fibers and matrix resins, have excellent strength, stiffness, or other characteristics and are used for various applications, for example, primary structure members of flying machines, automotive members, windmill blades, and chassis for various electronic machines. For such applications, particularly important physical properties mainly include physical strength, for example, impact strength, elastic modulus, flexural strength, and interlaminar toughness. In order to improve such physical properties, it is being devised to add a variety of fillers to a CFRP containing a matrix resin (for example, an epoxy resin component) and a carbon fiber. In particular, reinforcement of CFRP using polyamide fine particles is now being investigated variously.
Japanese Patent Application Laid-Open Publication No. 2014-145003 (JP-2014-145003A, Patent Document 1) discloses a pre-preg (an intermediate material for molding) containing a reinforcing fiber, an epoxy resin, and two kinds of polymer particles with different average particle sizes; of the polymer particles, a larger polymer particle having an average particle size of 10 to 30 μm has a glass transition temperature of 80 to 180° C. In working examples of this document, a polyamide fine particle is prepared by chemical pulverization in which a polyamide is dissolved in a solvent and then a poor solvent is added to the resulting solution to give a precipitate.
Japanese Patent No. 5655976 (JP-5655976B, Patent Document 2) discloses a pre-preg which consists of a composition containing a reinforcing fiber, a thermosetting resin, a crystalline polyamide, and an amorphous polyamide, wherein the composition contains a particle having a specific dynamic storage modulus and a glass transition temperature of 80 to 180° C. In working examples of this document, a polyamide fine particle is prepared by chemical pulverization in which a crystalline polyamide and an amorphous polyamide are dissolved in a solvent and then a poor solvent is added to the resulting solution to give a precipitate.
WO2015/033998 pamphlet (Patent Document 3) discloses, as a composition for a fiber-reinforced composite utilizable as a pre-preg, a composition containing a reinforcing fiber, a globular polyamide resin particle having an average particle size of 12 to 70 μm, and a matrix resin. In working examples of this document, a polyamide resin particle is prepared by forced emulsification in which a polyamide is melt-kneaded using a material incompatible with the polyamide.
Unfortunately, these polyamide particles fail to sufficiently improve a reinforcing effect by the reinforcing fiber. Further, the polyamide particles described in Patent Document 2, which contain two kinds of polyamide particles, need homogeneous mixing, and this results in difficult handling.